The requirement of drilling in very close proximity to adjacent wells in surface hole section has been common as field become more crowded. This is true especially in offshore mature field where the last wells are drilled on a dense platform. In Santan Field, East Kalimantan, conductor pipes were driven between the existing wells since sidetrack or platform extension options were not available at the time while there are still opportunity for infill and step out wells.

This situation introduces challenges on well construction in term of collision avoidance since the spacing between the wells are tight from surface point. The distance between slots is as low 1 meter from center-to-center, and 0.64 meter between wall-to-wall. Directional works was also required at shallow depth to kick of the well as per trajectory requirement.

The risk of unplanned intersections with adjacent well can lead to financial loss, personnel safety as well as environmental issue. A comprehensive risk assessment were conducted during the planning phase as the safety of drilling operation has been one of the main concerns. Mitigations plan were then formulated with the objectives to manage the negative consequences to acceptable level.

During the planning phase, detail anti-collision procedure was executed to evaluate the collision risk. On the field, several activities were carried out on adjacent wells prior to rig move in as mitigations measure: 1) Rig less resurvey, 2) Well integrity inspection, and 3) Well barrier placement. While drilling, following strategies were performed: 1) GWD utilization, 2) Monitoring on subject and adjacent wells, and 3) Collision-tolerant drilling bit application

The all-surface hole were drilled safely without any HSE or reliability issue. No major indications of well collision were observed. However, the drilling time took bit longer than usual performance due to drilling controlled manner for anti-collision precautions.

This paper explain how well collision mitigations was implemented in Santan Field, East Kalimantan, which can be a reference for further drilling as a successful case of top-hole drilling on a dense fixed platform. The method is expected to gain economic value, which is notably beneficial in mature field.

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